Solid-State Growth of One- and Two-Dimensional Silica Structures on Metal Surfaces

Crystalline or vitreous silica layers are new two-dimensional (2D) nanomaterials, which have shown surprising structural similarities with graphene and promise interesting properties. In this study, one-dimensional (1D) silica structures are formed on metal surfaces. In an in situ electron microscopy experiment it is demonstrated that lines of silica grow along step edges on metal surfaces. The growth of 1D silica occurs in competition with the formation of 2D networks and adopts the crystalline symmetry of the metal surface. Transformations between 1D and 2D structures are observed. Density functional theory calculations show that 1D silica is energetically favorable over 2D structures if surface steps prevail on the substrate. Our results indicate that lateral heterostructures with interesting properties may be developed on metal substrates

Solubility of Boron, Carbon, and Nitrogen in Transition Metals: Getting Insight into Trends from First-Principles Calculations

Efficient chemical vapor deposition synthesis of two-dimensional (2D) materials such as graphene, boron nitride, and mixed BCN systems with tunable band gaps requires precise knowledge of the solubility and mobility of B/C/N atoms in the transition metals (TMs) used as substrates for the growth. Yet, surprisingly little is known about these quantities either from experiments or simulations. Using first-principles calculations, we systematically study the behavior of B/C/N impurity atoms in a wide range of TMs. We compute formation energies of B/C/N interstitials and demonstrate that they exhibit a peculiar but common behavior for TMs in different rows of the periodic table, as experimentally observed for C. Our simulations indicate that this behavior originates from an interplay between the unit cell volume and filling of the d-shell electronic states of the metals. We further assess the vibrational and electronic entropic contributions to the solubility, as well as the role of anharmonic effects. Finally, we calculate the migration barriers, an important parameter in the growth kinetics. Our results not only unravel the fundamental behavior of interstitials in TMs but also provide a large body of reference data, which can be used for optimizing the growth of 2D BCN materials

<i>In Situ</i> Growth of Cellular Two-Dimensional Silicon Oxide on Metal Substrates

Crystalline hexagonally ordered silicon oxide layers with a thickness of less than a nanometer are grown on transition metal surfaces in an <i>in situ</i> electron microscopy experiment. The nucleation and growth of silica bilayers and monolayers, which represent the thinnest possible ordered structures of silicon oxide, are monitored in real time. The emerging layers show structural defects reminiscent of those in graphene and can also be vitreous. First-principles calculations provide atomistic insight into the energetics of the growth process. The interplay between the gain in silica–metal interaction energy due to their epitaxial match and energy loss associated with the mechanical strain of the silica network is addressed. The results of calculations indicate that both ordered and vitreous mono/bilayer structures are possible, so that the actual morphology of the layer is defined by the kinetics of the growth process

<i>In Situ</i> Growth of Cellular Two-Dimensional Silicon Oxide on Metal Substrates

Crystalline hexagonally ordered silicon oxide layers with a thickness of less than a nanometer are grown on transition metal surfaces in an <i>in situ</i> electron microscopy experiment. The nucleation and growth of silica bilayers and monolayers, which represent the thinnest possible ordered structures of silicon oxide, are monitored in real time. The emerging layers show structural defects reminiscent of those in graphene and can also be vitreous. First-principles calculations provide atomistic insight into the energetics of the growth process. The interplay between the gain in silica–metal interaction energy due to their epitaxial match and energy loss associated with the mechanical strain of the silica network is addressed. The results of calculations indicate that both ordered and vitreous mono/bilayer structures are possible, so that the actual morphology of the layer is defined by the kinetics of the growth process

Single-Layer ReS₂: Two-Dimensional Semiconductor with Tunable In-Plane Anisotropy

Rhenium disulfide (ReS₂) and diselenide (ReSe₂), the group 7 transition metal dichalcogenides (TMDs), are known to have a layered atomic structure showing an in-plane motif of diamond-shaped-chains (DS-chains) arranged in parallel. Using a combination of transmission electron microscopy and transport measurements, we demonstrate here the direct correlation of electron transport anisotropy in single-layered ReS₂ with the atomic orientation of the DS-chains, as also supported by our density functional theory calculations. We further show that the direction of conducting channels in ReS₂ and ReSe₂ can be controlled by electron beam irradiation at elevated temperatures and follows the strain induced to the sample. Furthermore, high chalcogen deficiency can induce a structural transformation to a nonstoichiometric phase, which is again strongly direction-dependent. This tunable in-plane transport behavior opens up great avenues for creating nanoelectronic circuits in 2D materials